1. Field of the Invention
The present invention relates to a display device which presents the eye of an observer with a virtual image of an image photographed by a video camera, computer graphic or other such electronic image.
2. Description of the Related Art
In order to achieve light weight and compactness in a display device which projects an image onto the eye of an observer as a virtual image, the use of a two-dimensional viewing means structured as compactly as possible is desired. Two-dimensional display means include a display which displays a two-dimensional image directly (e.g., which effects display by illuminating a two-dimensional liquid crystal display controlled on the basis of an image signal), and a scanning-type display which displays a two-dimensional image by using a scanner to scan light emitted from a point light source.
In order to make such display device compact, it is advantageous to make the incident light beam diameter presented to the observer as small as possible. Particularly in a device employing a scanning-type display means, the smaller the incident light beam diameter presented to the observer is made, the more lightweight and compact a rotating reflecting mirror or other such scanner can be made. Faster scanning is thereby afforded, a device can be made more lightweight and compact, and highly detailed image display can also be effected.
If the diameter of the incident light beam is made smaller than the pupil diameter of the observer, the amount of light reaching the retina of the observer does not change even if the pupil diameter of the observer changes. The image presented to the observer will consequently be an unnatural one differing from a realistic image, the reason being that the mechanism controlling the human pupil is extremely sensitive to changes in external brightness and reacts to external dynamic changes in brightness by changing the pupil diameter to regulate the amount of light reaching the retina.
For example, when a highly brilliant image meets the eye, its dazzling quality causes the pupil of an observer to contract, but when the diameter of the incident light beam is made smaller than the pupil diameter of the observer, the amount of light reaching the retina of the observer is not reduced, and the observer feels that the viewed image continues to change, becoming brighter. Conversely, even when an image changes to one of low brightness, the observer will be similarly presented with an unnatural sensation without purpose.
Under such conditions which differ from realistic conditions, wherein change in the pupil diameter of an observer does not function adequately to regulate the quantity of light, the visual function or nerve function of an observer may also be damaged. As the foregoing description provides, reducing the light beam diameter presented to the eye of an observer engenders a number of disadvantages. Yet there is no prior art which solves these several problems.